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The Mexican Pacific Ocean (MPO) includes the oceanic area of the northernmost region of the West coast of the Baja California Peninsula to the southern portion of Chiapas at the border with Guatemala. In this región are located the Gulf of California and the Gulf of Tehuantepec. The surface oceanic circulation in the MPO is seasonal with alternation in intensity and occupation area of the California Current, the Equatorial Countercurrent, the North Equatorial Current, and the system of the Costa Rica Coastal Current, which together determine the presence of marine fauna of different biogeographic affinities. The collection of cephalopod paralarvae (PL, squids and octopus) with plankton nets has proved to be one of the best tools to determine diversity in this group. Our objective was to determine the cephalopod species composition in three areas of the MPO, based on the presence of their planktonic paralarvae. The zooplankton samples analyzed were collected by means of oblique tows during 14 oceanographic cruises. Four cruises were made in front of the west coast of the Baja California Peninsula (WCBCP, 1997-1999), eight in the Gulf of California (GC, 2004-2007), and two in the Gulf of Tehuantepec (GT, 2008). We recorded 65 species in the three areas, included in 14 families. The most important in the WCBCP were the family Ommastrephidae (54%), Onychoteuthi­dae (17.6%), and Pyroteuthidae (4%); in the GC were Pyroteuthidae (41.6%), Ommastrephidae (37.2%), and Enoploteuthidae (7.9%), while in the GT the Enoploteuthidae (39.1%), Ommastrephidae (30.5%), and Cranchiidae (13.2%) were the most important. Ecological indexes (based in total abundance of species by area) indicate a higher paralarvae abundance in the GC with a richness S=44, followed by the WCBCP (S=36), and the GT (S=16). The WCBCP had the highest diversity (H´=3.17) and evenness (J´=0.61). In the GC dominance (D=0.30) was determined by three taxa, in comparison with the GT (D=0.18) where six taxa dominated. The PL of tropical-subtropical affinity were the most abundant, temperate ones were scarce, and only one cosmopolitan species was recorded in the three areas. The ENSO 1997-2001 influenced the presence and abundance of tropical species in the WCBCP; in the GC seasonality determined the presence of the temperate component only during winter, while in the GT the sampling limitations do not allow further explanation.

Palabras clave: mexican Pacific Ocean; Body growth; Gulf of Tehuantepec; Paralarvae

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